138 Adkinson. — Some Features of the Anatomy of the Vitaceae. 
ments of the xylem is the means by which the herbaceous stem has developed 
as a result of the influence of the leaf-trace. In Vitis the development of 
broad rays has progressed synchronously with the reduction of radial 
parenchyma tissue within the bundle. So the intrafascicular rays of all 
the Vitis species investigated, with the exception of V. calif ornica, Benth., 
have been transformed into radial wood parenchyma, or they have entirely 
disappeared except as vestiges in the leaf-trace segment of the first annual 
ring and particularly in that of the seedling. V. calif ornica , Benth., is there- 
fore the most primitive American species of Vitis examined, and those species 
which retain vestiges of the primitive rays in the adult or the seedling are 
more conservative of ancestral characters than those forms in which all trace 
of the rays has been lost. 
The tendency of the bundle to a reduction of lignified tissue is shown 
in the increase of the broad rays at the expense of the wood fibres, and in 
the abundance of septate tracheides which are a stage in the transformation 
of xylem tissue into parenchyma. With the reduction of lignified tissue 
advances the elimination of radial parenchyma within the xylem. By this 
process the condition of Ampelopsis and Cissus is achieved. The develop- 
ment of the vine habit in the Vitaceae is an approach to the herbaceous type 
of stem. Like the herbaceous habit, it is brought about by localization 
of ray parenchyma and restriction of protoxylem and lignified tissue to 
definite xylem segments in the stem. By the loss of intrafascicular and 
finally of fascicular cambium, the transformation of the woody cylinder to 
the herbaceous stem would be complete. This mode of development is 
caused by the increased activity of the leaves and the need for greater 
storage capacity. The broad rays, the pith sheath, the elements of the 
phloem, all serve this purpose. The libriform fibres segregated in bundles 
supply the necessary tensile strength for the vine, while the broad parenchyma 
plates afford great flexibility. 
Thus the wood structure of the Vitaceae is intermediate between that 
of the arboreal and fruticose types and the herbaceous stem. The course 
of evolution in the family constitutes another link in the chain of facts 
which supports the new theory of the origin of the herbaceous habit in 
plants. 
Conclusions. 
1 . The ancestors of Vitaceae were shrubby or arboreal forms, in the 
central cylinder of which occurred interfascicular broad rays and intra- 
fascicular linear rays. The genus Leea is the most primitive living repre- 
sentative of the family. 
2. The linear rays of the mature normal wood of all species of Vitis 
examined have disappeared, except in V, calif ornica, Benth., which is on 
these grounds the most primitive member of the genus. 
